Bicycle has become a popular exercise, amusement and leisure tool. More and more people rides bicycles in daily life or in leisure time. It is not only improve the health of the driver, but also provide the pressure feeling to driver because in driving, the driver can see the beautiful scenery in driving path and breathes clean air.
Thus it is important that the cushion of the bicycle must make the driver feel comfortable with less fatigue driving so as to have a better affect in driving. As a result, the structure of the cushion and seat tube become important in design of the bicycle. The cushion must be soft and have preferred sock absorption ability. The seat tube must be designed to suit the pose, habit and size of the driver. In U.S. Pat. No. 5,466,042, the set tube is installed with a positioning seat which includes a first clamping unit and a second clamping unit. Two covers are transversally installed between the clamping units. One side of the seat tube is installed with a screw unit and another side thereof is installed with another screw unit. The screw unit has a teethed disk. Each screw unit passes through a cover and is assembled to the clamping unit and the positioning seat. In the unit, as the teethed disk is driven, one screw units will be tightened or released so as to adjust the orientation and position of the cushion.
However the structure has complicated structure and higher cost. The assembly is tedious and in adjustment, the screw units at two sides must be screwed at the same time as to adjustment the cushion. The operation is tedious and time consumed. Besides, in maintenance or repair, the whole structure must be detached for updating the parts, and then they are assembled again and the adjustment is done again for having a desiring orientation and position. Thus the prior art structure has longer manufacturing time, and greater producing cost, while the assembly and maintenance work are time consumed and tedious.